1. Field of the Invention
The present invention relates to a low-temperature sintered conductive metal film and a preparation method thereof.
2. Description of the Related Art
Generally, technology developments for forming fine patterns for wiring formation is receiving attention as demands increase for high reliability and high conductivity for forming an electrode or a circuit of display, FPCB, RFID, etc.; for a larger screen, high efficiency, and high resolution for display; and for using a flexible substrate. In the mean time, competitions for various flat-panel display types such as PDP and LCD have been intensified that the efforts have been made to reduce the cost of raw materials including electrode materials and the cost of processing these. Also, with various portable electronic devices getting smaller, chips used for the devices are required to have a higher density and a higher integrity.
One of the general methods for forming a conductive layer such as wiring pattern, etc. on a substrate embedded in various electronic devices is the metal plating. Another methods include the heat curing of a resin after forming a wiring on a substrate by applying and printing a conductive paste, which is a liquefied thermosetting resin material, with electro-conductive powder dispersed therein, or a thin film forming method which applies a ultra-fine metal particle dispersion liquid, which is dispersed uniformly into an organic dispersion medium, onto a semiconductor substrate and then heats the liquid to eliminate an organic solvent and fuse the ultra-fine metal particles. However, the plating method has a shortcoming of a low productivity, because a growth speed of a plated film from a metal ion is slow and accordingly considerable time is required to form a thick (more than about 10 μm of thickness) conductive film, conductive layer, or layer short. And the methods of forming a conductive layer by applying or printing the conductive paste or the ultra-fine metal dispersion liquid also have a shortcoming in precisely controlling the thickness and the forming position of the conductive layer. In particular, the conductive paste comprising a resin and electro-conductive powder has a difficulty in forming the conductive layer with a high precision in terms of the forming position and shape, because the conductive layer has a relatively higher viscosity (approximately 100 mpa·s at 25° C.). But if resin element is not included in order to reduce the viscosity of the ultra-fine metal particle dispersion liquid, cracks may be created in a conductive layer and the adhesion of the conductive layer to the substrate may deteriorate for forming a thick conductive layer.
Meanwhile, an inkjet technology is a new type preparation process, which has been developed amid the pursuits of productivity, cost reduction, and creation of new industrial fields with the display industry becoming larger and the process simplified. An inkjet printing is a contactless technology, which prints a pattern by means of a jetting ink ejected from a nozzle of a print head. For the inkjet printing technology, a print head technology has been developed a lot, but designing an ink has still remained as a challenge. The ink is required to meet sophisticated physiochemical characteristics to obtain optimum driving conditions and gain durability of a printing system and a desirable printing pattern. In the case of a metal ink, a preparation for homogeneous and stable nanoparticles is preferred of all things.
A metal ink for inkjet, as a material mainly forming a fine conductor or a thin conductive film, uses metal nanoparticles with the particle size of a few or a few dozens of nanometers. Recently, researches to form, for example, fine conductors by means of the inkjet technology after preparing the metal ink by using silver nanoparticles are in progress, but due to a high-cost of production involved in using silver particles, there are many limitations to the industrial applications. Therefore, a need for copper nanoparticles, as a low-cost material replacement with a relatively high conductivity, has been discussed continuously, but preparing stable copper nanoparticles may be challenging due to a low stability, i.e., a high oxidativity and developing a preparation of stable copper nanoparticles in a uniform particle size is still insignificant because the growth of the particles is too fast during the preparation of the nanoparticles.
Korean Patent No. 10-0911439 discloses a waterborne conductive ink for inject added with a dispersion agent and dispersion solvent of a nano silver colloid solution comprising nano silver particles with the size of 20 nm or less. Using the silver nanoparticles may make the handling easy in terms of safety and environment and is desirable for storage and dispersion stability, and may make the preparation of a conductive ink possible for printing by the inkjet method. Still, the production cost may be high due to the use of the expensive silver.
Korean Patent No. 10-0833869 discloses an ink composition comprising a metal nanoparticle mixture of copper nanoparticles and silver nanoparticles and an organic solvent. The ink composition comprising the metal nanoparticle mixture of the copper nanoparticles and silver nanoparticles and the organic solvent may control an ion migration phenomenon effectively on the conductive wiring comprising silver as a material without a decline in conductivity. But, using the copper nanoparticles may pose problems of securing the stability of the copper particles and of performing a heat treatment at a high temperature after printing an ink due to a high sintering temperature of copper.
Accordingly, the inventors of the present invention completed the present invention by developing a conductive metal film presenting a low sintering temperature after mixing metal nanocolloids, metal salts, and polymers, preparing a metal ink whose nanoparticles are stable, and printing the metal ink.